The proposed work will involve the measurement of HMG-CoA reductase, 7 alpha-hydroxylase, and 12 alpha-hydroxylase in normal subjects, patients with chronic cirrhotic liver disease and in patients with type II hypercholesterolemia. Comparisons will then be made with the rates of these enzymatic reactions and the rates of synthesis of cholic acid and chenodeoxycholic acid. We will also be determining the metabolism of bile acids in pediatric patients with intrahepatic bile duct anomalies (intrahepatic bile duct atresia) using isotopic dilution kinetics. Comparisons will be made, in the same individuals, after treatment with cholestyramine and phenobarbital. Studies have been initiated to investigate the Beta- oxidation of C27 bile acids into C24 bile acids by mitochondrial preparations.